Why is it useful for historian to base certain studies on the analysis of historial periods

Historians study periods of time because it organizes history based on major events or themes of the period. Each period in history creates a snapshot of the world or a region during that time.

Belgrade fell again in October 1915, as the Bulgarians made their way into Niš and Kosovo. All looked lost for the Serbs, so the decision was made to retreat through the mountains of Montenegro and Albania in the hope of making it to Greece, the nearest stronghold of Serbia's allies.

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